Free machining steel with sulphur plus tellurium and/or selenium



United States Patent 3,152,890 FREE MACHINING STEEL WITH SULP PLUS TELLURI UM AND/0R SELEN- Michael 0. Holowaty, Gary,.lnd., .assignor to Inland Steel Company, Chicago, Ill., a corporation of Delaware .No Drawing. Filed Nov. 14,, 1963, Ser. No. 323,590 2 Claims. (Cl. 75-123) tion Serial No. 146,312 is a continuation-in-part of the present inventors abandoned application Serial No. 8,918,.

filed February 16, 1960, in turn a continuation-in-part of abandoned application Serial No. 725,501, filed April 1, v

The use of relatively large amounts of tellurium and/ or selenium to increase the machinability of steel is expensive. The subject steel has superior machining characteristics imparted thereto by relatively inexpensive amounts of tellurium and/or selenium supplemented by sulphur. The total tellurium and/ or selenium content is about between 0.02-0.10 wt. percent and, alone, partially improves the machinability of the steel. With a tellurium and/ or selenium content in this range it is important that the sulphur, in order to impart a substantial additional increase in machinability to the steel, be in molecular excess relative to the tellurium and selenium. For example, assume a tellurium and selenium content of 0.04 wt. percent of each. The ratio of atomic weights of sulphur to tellurium is 32.07 to 127.5 or about 1 to 4, and the ratio of atomic weights of sulphur to selenium is 32.07 to 79.2

' .or about 2 to 5. Accordingly, a molecular equivalent of sulphur relative to a tellurium content of 0.04 wt. percent is-about 0.01 wt. percent, and a molecular equivalent of sulphur relative to a selenium content of 0.04 wt. percent is about 0.016 wt. percent. Thus, a sulphur content in excess of its molecular equivalent relative to the tellurium and selenium would be about 0.03 wt. percent or better. Assuming a content of 0.04 wt. percent tellurium alone or selenium alone, a sulphur content of 0.02 wt. percent or more would satisfy the criterion.

Although the sulphur is present in molecular excess relative to the tellurium and/ or selenium, the weight of the sulphur does not exceed the total weight of the tellurium and/ or selenium, themselves present in relatively inexpensive amounts not exceeding 0.10 wt. percent in total. Accordingly, the total weight percent of both the sulphur and the tellurium and/or selenium is relatively small, thereby reducing the likelihood of adverse effects (such as hot shortness) attributable to a high sulphur and/or tellurium and/or selenium content. To further reduce the possibility of hot shortness, it is important that the subject steel have a manganese content exceeding 0.60 wt. percent.

Because the subject steel relies upon relatively inexpensive amounts of tellurium and/ or selenium and preferably no greater amounts of sulphur than tellurium and/ or selenium to impart machinability thereto, it is importantthat the silicon content be low so as not to offset the increased machinability imparted to the steel by the limited amounts of sulphur and tellurium and/or selenium. Accordingly, the subject steel contains a silicon content of 0.05 wt. percent or less.

By utilizing an inexpensive tellurium and/ or selenium addition in the range described supplemented by a sulphur 3,152,890 Patented Oct. 13, 1 964 content in the amount described together with a silicon content of less than 0.05 wt. percent and 'a'manganese-con- 1 tent exceeding 060 wt. percent, there is provided arelatively inexpensive tellurium and/or selenium-containing steel which is readily .machinable and which does not display the symptomatic adverse effects (such as hot shortness) otherwise characteristic of steelscontaining tellurium and/ or selenium and/ or sulphur.

Typical examples of steels having compositions (expressed in wt. percent) within the range of the present invention are as follows:

Table A.--Tellurium Steel Steel Steel Steel I II III IV Table B.Selenium Steel Steel Steel Steel I II III IV 0.16 0.16 0.10 0:70 0 65 0. 60 0.011 0 02 0. 04 0. 05 0 05 0.04 0 08 0 05 0. 03 S 0.06 0 04 0.03 Percent Molecular Equivalent of S 188 200 250 Steel Steel Steel Steel I II III IV With reference to the above tables, it should be noted that the sulphur content of all the steels is in molecular excess relative to the tellurium and/ or selenium content, and the Weight of the sulphur is no greater than the weight of the tellurium and/ or selenium. The molecular excess of the sulphur in Steels H and IV of Table A, in Steel IV of Table B and in Steels III and IV of Table C is or better, this being a preferable embodiment of the present invention.

There has thus been described a relatively inexpensive, readily hot workable tellurium and/ or selenium-contain ing free machining steel characterized by:- a relatively inexpensive amount of tellurium and/ or selenium; a molecular excess of sulphur relative to the tellurium and/ or selenium with the weight of the sulphur being no greater than the Weight of the tellurium and/ or selenium; a silicon itations should be understood therefrom, as modifications the minimum wt. percent of said sulphur being in mowill be obvious to those skilled in theart. lecular excess of the Wt. percent of said first addition;

What is claimed is: no more than about 0.05 silicon; 1. A free machining, at least partially hot worked steel and the balance Consisting essentially 0f ironsi ti ti ll f i Wt t; 5 2. A steel as recited in claim 1 wherein the molecular 0104113 carbon; excess of sulphur is 150%. 0.60-0.75 manganese; 001L004 phosphorus; v v v References Cited in the file of this patent 0.02-0.10 of a first machinability increasing addition UN STATES PATENTS selected from the group consisting of tellurium, se- 10 2,009,714 P l Jul 30 1935 leniurn, and tellurium plus selenium; 2,182,758 Hard Dec 5, 1939 sulphur in wt. percent no greater than the wt. percent 2,485,358 Case Oct. 18, 1949 of said first addition; j 2,397,078 Nishikiori July 28, 1959 

1. A FREE MACHINING, AT LEAST PARTIALLY HOT WORKED STEEL CONSISTING ESSENTIALLY OF, IN WT. PERCENT: 0.10-0.18 CARBON; 0.60-0.75 MANGANESE; 0.012-0.04 PHOSPHORUS; 0.02-0.10 OF A FIRST MACHINABI-LITY INCREASING ADDITION SELECTED FROM THE GROUP CONSISTING OF TELLURIUM, SELENIUM, AND TELLURIUM PLUS SELENIUM; SULPHUR IN WT, PERCENT NO GREATE THAN THE WT. PERCENT OF SAID FIRST ADDITION; THE MINIMUM WT. PERCENT OF SAID SULPHUR BEING IN MOLECULAR EXCESS OF THE WT. PERCENT OF SAID FIRST ADDITION; NO MORE THAN ABOUT 0.05 SILICON; AND THE BALANCE CONSISTING ESSENTIALLY OF IRON. 